[MeL] Make Node::setID protected instead of privat.

This is needed for the GMSH interface.

MeshLib/Node.h

@@ -73,7 +73,7 @@ public:
         return Node(_x[0]-v[0], _x[1]-v[1], _x[2]-v[2]);
     }
 
-private:
+protected:
     /// Update coordinates of a node.
     /// This method automatically also updates the areas/volumes of all connected elements.
     void updateCoordinates(double x, double y, double z);